1. Field of the Invention
This invention relates to a monitoring system incorporated in a temperature controller or the like to monitor an object and present information about the state of the monitored object on a display device incorporated therein.
2. Description of the Related Art
Japanese Patent Application KOKAI Publication 2004-126732 (referred to as Patent Document 1) discloses a temperature controller for controlling temperature of a variety of temperature environments, etc. The temperature controller disclosed has a function of controlling the temperature of an object by obtaining a control output (MV value) to be supplied to a heating•cooling device on the basis of a temperature (PV value) of the object detected by a temperature sensor such as a thermocouple or a resistance thermometer and a set temperature (SP value), while presenting a numerical display of the detected temperature. Generally, the temperature controller of this type has also a function of detecting abnormalities, and when detecting an abnormal temperature of the temperature-controlled object, a failure of the temperature sensor or the like, presents a warning display and supplies event information to the outside to notify the detected abnormal event. The warning display is presented, for example on a display device for presenting a numerical display of temperature.
As an example, that a failure of the temperature sensor to be detected can be a conductor breakage in a sheathed thermocouple. There are cases such that a conductor becomes broken due to thermal stress acting in filling material thereof only when its temperature rises high, and returns to a conductive state when the temperature drops. In such cases, since the conventional temperature controller is configured to present a warning display only when a conductor breakage is detected, there is a risk that the warning display is overlooked so that the conductor breakage in the sheathed thermocouple fails to be recognized, unless the display device is always monitored.
Further, there are temperature controllers arranged such that when a failure of the body of the temperature controller is detected, event information is generated and transmitted to the outside, for example by means of a latch circuit configured to retain the output state resulting from receipt of an abnormality detection signal, thereby continuing to output a latch signal until reset. In such temperature controllers, however, the failure cannot be recognized unless event information supplied from the temperature controller to the outside is monitored by means of an external device such as a main control device. Further, even when the failure of the body of the temperature controller is gone so that outputting of an abnormality detection signal stops, transmission of event information continues unless the latch circuit retaining the output state resulting from the receipt of an abnormality detection signal is reset. This prevents an accurate grasp of the present situation.